A light-emitting device including an organic EL element can be configured to have a planar shape and can emit light of white color or a color close thereto. The light-emitting device including an organic EL element may thus be used as light sources of lighting apparatuses for illuminating space such as a living environment, or may be used in applications for backlight devices of display devices.
Currently known organic EL elements, however, have insufficiently low efficiency for the aforementioned illumination purposes. Thus there is a demand for improving light extraction efficiency of the organic EL elements. A known method for improving the light extraction efficiency of an organic EL element is to provide a variety of types of concavo-convex structures on a light-emitting surface of a single side emission type organic EL element. For example, it has been proposed to provide a structure layer having a concavo-convex structure on a light-emitting surface of an organic EL element (see Patent Literature 1). This concavo-convex structure can achieve favorable collection of light to improve the aforementioned light extraction efficiency.
Furthermore, studies have been made regarding light-emitting devices of see-through type in which transparent electrodes are employed as the electrodes of an organic EL element and thereby the other side of the light-emitting device can be observed therethrough (see Patent Literature 2).
Technologies of Patent Literatures 3 and 4 have also been known.